The present invention relates to an arithmetic unit for executing an arithmetic process with respect to data in which a word is not standard 2n-bit wide.
Some devices for outputting or processing image and audio, use data in which a word is not standard 2n-bit wide. This is for improving image and audio quality, or for providing image and audio with any additional information. Such devices are exemplified by so-called third generation mobile phones or information processors for generating image data with various tones. This type devices include a digital signal processor (hereinafter, referred to as DSP) or other type of arithmetic unit. Using such devices, a bit width for a word is converted into a standard 2n-bit for various arithmetic processes.
In the below, by taking a DSP mounted in a third generation mobile phone as an example, an arithmetic unit of a conventional type is described.
The third generation mobile phone uses a DSP for extracting signals in several specific bands out of a wide frequency band for achieving communications always good in condition. From the extraction result, one specific frequency band especially high in reception sensitivity is selected for communications. Here, for such signal extraction, the DSP uses a technique called digital matched filter (hereinafter, referred to as DMF) algorithm, which will be described later, to emphasize path intensity of signals in specific bands, and thereby extracts signals in the specific bands.
The DSP of a conventional type outputs 16-bit data at a time from memory to an arithmetic logic unit (hereinafter, referred to as ALU). The issue here is that, an arithmetic process does not require all of the 16-bit data but only 10-bit. It means that the conventional arithmetic unit wastefully outputs 6-bit data to the ALU at a time.
The ALU includes a 32-bit-wide arithmetic section (not shown), but is only utilizing a part thereof, i.e., section of 10-bit wide. It means that the arithmetic section of 22-bit wide goes to waste with the conventional arithmetic unit.
As such, when executing an arithmetic process using data in which a word is not standard 2n-bit wide, the arithmetic unit of the conventional type causes waste of an arithmetic section in an ALU or memory usage. This is because of an unused part arranged between I part data and R part data. Especially, it is a problem that at the time of executing an operation process using the DMF algorithm, efficient use of arithmetic capability and memory cannot be fully achieved.